Give equation which relate $c,{\mu _0},{ \in _0}$.

The electric field associated with an $e.m.$ wave in vacuum is given by $\vec E = \hat i\,40\,\cos \,\left( {kz - 6 \times {{10}^8}\,t} \right)$. where $E$, $z$ and $t$ are in $volt/m$, meter and seconds respectively. The value of wave factor $k$ is ....... $m^{-1}$.

The nature of electromagnetic wave is :-

An electromagnetic wave of intensity $50\,Wm^{-2}$ enters in a medium of refractive index $’ n’$ without any loss . The ratio of the magnitudes of electric fields, and the ratio of the magnitudes of magnetic fields of the wave before and after entering into the medium are respectively. Given by

Light with an energy flux of $25 \times {10^4}$ $W/m^2$  falls on a perfectly reflecting surface at normal incidence. If the surface area is  $15\,\, cm^2$ the average force exerted on the surface is

A TV tower has a height of 100 m. The average population density around the tower is 1000 per $km^2$. The radius of the earth is $6.4 \times {10^6}$m. the population covered by the tower is